The present invention relates generally to cooking apparatus and in particular to a steam cooker for processing and reconstituting food items.
A steam cooker generally consists of a cooking chamber and a source of steam. Heat from the steam is transferred directly to food items placed in the cooking chamber. As heat is transferred to the food items, the steam condenses and the resulting condensate may or may not be drained from the chamber during the cooking cycle.
Cooking food in the presence of steam has been found to be very efficient and to have a minimal affect on taste, texture, color and other characteristics of the food. The moist cooking environment provided by the steam, prevents food from dehydrating as it often does in radiant heat or convection air type ovens.
Because the steam, which completely surrounds the food contains an enormous amount of heat, this type of oven will cook food very fast and is especially useful for thawing frozen foods. Generally, the steam for cooking will be in the vicinity of 212.degree.-248.degree. F. This relatively moderate temperature coupled with the heat exchange efficiency between the steam and the food allows food items to be thawed very quickly within the oven without adversely affecting food quality. Because of this operational flexibility and the ability to process large amounts of food in relatively short spans of time, steam cookers are very popular in commercial food establishments.
Early steam cookers were usually rather large devices having multiple cooking compartments which were supplied with steam sources separate from the steam cooker unit. A need for a compact, counter top steam cooker for small commercial establishments was recognized and various constructions to fill this need have been proposed.
One such unit includes a steam generating means as part of the cooking compartment. It includes a reservoir of water below the cooking chamber which is boiled to produce steam for cooking. As the water boils, the steam rises and flows into the cooking compartment to heat food placed therein. As the steam cools, the condensate returns to the reservoir.
In another proposed unit, a separate steam generator produces the necessary cooking steam. The steam generator is of the electrode type and the steam produced is generally admitted to the cooking chamber through a valve controlled conduit. In this steam cooker, the operator must select an interval of time over which steam is produced and allowed to enter the cooking chamber. Because the steam is produced at a relatively constant rate, the operator must carefully select the cooking time to avoid overcooking the food.
Some of these prior steam cookers utilize an electrode-type heater for producing steam in the steam generator. This type of heater usually consists of a pair of spaced electrodes suspended in a reservoir of water. When voltage is applied, water in the current path between the electrodes is heated. The amount of heat generated is, in part, dependent on the depth to which the electrodes are immersed in the reservoir and the conductivity of the water. For this reason, it is imperative that steam generators of this type have precise water level control and water conductivity compensation to insure a uniform rate of heating.
The production of steam in the prior steam cookers, in general, cannot be varied. Steam is produced and conveyed to the cooking chamber throughout the cooking cycle at a rate limited only by the capacity of the steam generator or the steam conduits. Many foods, especially frozen varieties, can only accept heat from the steam at a specific rate. Heat that cannot be absorbed by the food is usually exhausted as excess steam without making a contribution to the heating process. The production of steam in excess of that required is both energy and water wasteful.
One prior art unit attempted to overcome this problem, at least partially, by operating the steam cooker at approximately 12 psi above atmospheric pressure. In the past, it has been found that the use of pressurized steam increases the heat exchange rate between the steam and the food being processed. The use of pressurized steam, however, adds to the complexity of the steam cooker and only partially solves the shortcomings of the prior units. Certain safety features must be incorporated on these types of steam cookers to guard against the opening of the cooking chamber door when under pressure and, therefore, precludes, a user from observing the cooking progress of the food. The operator must wait for the cooking cycle to terminate and for the pressure to be released before the door can be safely opened. Additionally, a multitude of safety features is normally required to prevent excessive pressure build-up in the generator and in the cooking chamber.
The prior steam cookers suffer from a second shortcoming, also related to the inability to control the steam production rate on these cookers. It is often desirable to keep food warm until it can be served, which in some cases may be as long as thirty minutes. The prior steam cookers are unable to provide this function. At the conclusion of a cooking cycle in these prior units, the production of steam terminates and if the food is left in the cooking chamber it will begin to cool. If, however, the cooking cycle is extended in an attempt to keep the processed food warm, the food will be overcooked by the excessive amount of steam entering the cooking chamber.
Another problem associated with prior steam cookers is a gradual build-up of scale and corrosion in the steam generator. Many of the prior units do not address this problem at all and therefore the steam generators in these units require periodic service to remove the deposits. Some units provide an automatic or manual boiler blowdown feature in an attempt to minimize the formation of scale. If the scale is allowed to accumulate, the heating efficiency of the boiler heater will be impaired, and more importantly, the deposits may eventually block or excessively restrict conduits and valving communicating with the generator. Draining or "blowing down" the steam generator after each use will only retard the accumulation of scale but will not totally elminate the problem.